Multicast/Broadcast Service (“MBS”) in WiMAX Networks is a service that allows the distribution of data to a group of Mobile Subscribers (“MSs”). IEEE 802.16e standard introduces the notion of MBS_ZONE—aggregation of multiple Base Stations (“BSs”) wherein an MBS SF (“Service Flow”) having a certain SFID (Service Flow Identification) is mapped onto the same Connection Identifier (“CID”) (although in some applications this is done only when there is an identical communication to transmit). In other words, the term “MBS_ZONE” does not typically relate to an area as the same Base Station may belong to more than one MBS_ZONE. Instead, it relates to the mapping of MBS SFIDs onto certain CIDs to enable synchronous broadcast of the same data over the same subchannels at the same time. This technique greatly improves the mobile terminals ability to receive data correctly due to increased energy of the combined signal that each mobile terminal received simultaneously from multiple Base Stations.
MBS Service-Flow (“SF”) carries information to a set of MSs. Typically there are two methods to access a group of MSs for the provisioning of MBS:                Single-BS: Transmission of data over a single Base Station (“BS”) in the network. The SF is mapped to a Connection Identifier (“CID”) within a specific BS, i.e., the CID is uniquely specified on a “per BS basis”.        Multi-BS: Transmission of data over a plurality of BSs in the network in a synchronized manner. The SF is mapped to a CID unique within a zone at which the service is provided, referred to hereinafter as an “MBS_ZONE”.        
The establishment of an MBS connection is typically carried out in a way similar to the way by which unicast connections are established, while the MS registers to the network.
Upon completion of the network entry (“NWE”), the MS is provided with the relevant Multicasting Connection Identifiers (“MCIDs”) and/or with the relevant Logical Channels Identifiers (“LCID”), enabling it to receive the MBS, and this service, is maintained regardless of the current mode of the MS (Normal/Sleep/Idle), so that MBS data is transmitted and received regardless of the MS current operation mode.
The Multi-BS access method enables an MS to receive the MBS content, after having successfully registered and the connection established, from several BSs. As explained above, this transmission method requires that the group of BSs participating in the same Multi-BS-MBS service to be synchronized so that data shall be transmitted by all these BSs simultaneously, and to use the same CID and Security Association (“SA”). It should be noted that the MS does not have to be registered at the specific BS from which it receives MBS transmissions.
As was mentioned hereinbefore, an MBS_ZONE identifier is used to indicate the group of BSs which use the same CID and SA to distribute an MBS SF. MBS_ZONE can be advertised by the BS in DCD messages, also it can be delivered upon establishment of MBS connection and it can be extracted from the MAP_MBS_IE.
Logical Channels are used to distinguish between logical MBS connection for each MBS content delivered within the multicast connection. When used, every MBS content ID is assigned with a Logical Channel Identification (LCID). When an MBS context (within an MCID) is delivered the respective LCID is indicated. Typically, the use of LCIDs and content IDs is vendor specific and depends on the application-layer utilization. When an MS moves from one MBS_ZONE to another and when LCIDs are used, LCID should be re-assigned together with the MCID.
Obviously an MBS_ZONE may include one or more BSs, and a BS may have multiple MBS_ZONE identifiers.
However, one of the drawbacks of the currently known systems is the impact upon the service received by an MS moving from one MBS_ZONE to another, as when the MS detects that it moved to a new MBS_ZONE, it is required to update the MBS Connections IDs (“MCID”s) to match those of the new MBS_ZONE. This updating procedure takes time and while being carried out, it disturbs the reception of all multicast data. Upon entering the new MBS_ZONE, the MCIDs update may be performed either through Location Update (“LU”) procedure (e.g. if the MS is currently in Idle-Mode), by initiating Handover (“HO”) procedure, or by carrying out a complete network entry.